1. Field
This invention relates to audiological screening and testing methods. More particularly, it relates to a phase analysis system method and apparatus employing audiological screening via statistical phase analysis of otoacoustic emissions (OAE's), which are signals that are generated by the hair cells of a functioning inner ear in response to acoustic stimuli as a result of the non-linear properties of the cochlear amplifier.
2. State of the Art
Various audiological screening and testing methods are known. For the hearing testing of infants and small children, measurement systems based on the principle of evoked potentials or otoacoustic emissions via signal averaging and individual evaluation by a tester reviewing various wave pattern hearing responses on a display screen are often employed. Because these types of examinations are expensive, and require skilled evaluators, the results often are dependent upon the subjective skills of the evaluator. To overcome these subjective testing limitations, various signal display and evaluation apparatus, such as Kemp, PCT/GB/00030, published Aug. 7, 1981, entitled "Hearing Faculty Testing Apparatus, were developed. These conventional display methods employ methods of frequency and amplitude analysis of otoacoustic emissions (OAE's) signals generated by the inner ear in response to various tones. The frequency and amplitude of the OAE signals are picked up by a microphone and fed into a wave pattern display for measurement and manual or statistical analysis by an operator, see Zoth, DE 4441127A1 published May 23, 1996. These methods and devices may also employ averaging, where a number of signal intervals following the stimulation ("sweeps") are added synchronously with the stimulus, thus improving the signal-to-noise ratio until the emissions are detectable. These other machines thus require an experienced examiner to make a decision based on a number of objectives and subjective criteria such as the frequency spectrum, typical curve morphology and time distributions of the measured signals. The danger in using a normal averaging procedure is that any waveform can be produced by chance. To guard against this, other commercial systems have added additional features such as correlation of two quasi-simultaneous measurements. While this has proven valuable, the amount of correlation depends on the frequency spectrum of noise and signal, which differs from one measurement to another. As a consequence, a given correlation cannot be used exclusively as the criterion for the presence of emissions.
The invention described below provides an improved otoacoustic emissions testing and screening apparatus and method based on a phase analysis system of an analogue signal to provide a "pass"/"fail" or "pass"/"refer" type of response, which is more suitable for automated evaluation without the need for highly trained evaluators.